mTOR signaling in cancer cell motility and tumor metastasis

XTP8 Promotes Ovarian Cancer Progression by Activating AKT/AMPK/mTOR Pathway to Regulate EMT

Ovarian cancer (OC) ranks as the fifth leading cause of cancer-related death in women. The main contributors to the poor prognosis of ovarian cancer are the high rates of recurrence and metastasis. Studies have indicated a crucial role for hepatitis B virus X Ag-Transactivated Protein 8 (XTP8), a protein containing the DEP domain, in various cellular processes, including cell growth, movement, and differentiation, across several types of cancers. However, the role of XTP8 in ovarian cancer remains unclear. We observed elevated expression of XTP8 in ovarian cancer. Silencing XTP8 inhibited cell proliferation, promoted apoptosis, and yielded contrasting results in cells overexpressing XTP8. Furthermore, XTP8 facilitated ovarian cancer invasion and migration, triggering epithelial-mesenchymal transition (EMT). Mechanistically, XTP8 silencing led to reduced phosphorylation levels of AKT, increased p-AMPK levels, and decreased p-mTOR levels, while XTP8 overexpression exerted the opposite effects. Additionally, the activation of p-AMPK rescued the promoting effect of XTP8 on EMT in ovarian cancer cell lines, indicating that XTP8 acts as an oncogene by modulating the AKT/AMPK/mTOR pathway. Through transcriptome sequencing to identify downstream targets of XTP8, we found that XTP8 influences the expression of Caldesmon (CALD1) at both transcriptional and translational levels. CALD1 can be considered a downstream target of XTP8. The collaborative action of XTP8 and CALD1 activates the AKT/AMPK/mTOR pathway, regulating EMT to promote ovarian cancer progression. Inhibiting this signaling axis might represent a potential therapeutic target for ovarian cancer.

The inhibitory effect of LINC00261 upregulation on the pancreatic cancer EMT process is mediated by KLF13 via the mTOR signaling pathway

PURPOSE

The long noncoding RNA LINC00261 was reported to be involved in carcinogenesis and has been validated as a tumor suppressor in pancreatic cancer (PC); however, how LINC00261 is regulated has not been fully examined. Here, we attempted to investigate the upstream and downstream targets of LINC00261 in PC.

METHODS

LINC00261 expression in PC tissues was examined by the Gene Expression Omnibus (GEO) datasets and the Gene Expression Profiling Interactive Analysis (GEPIA) database. The quantitative reverse transcription polymerase chain reaction (qRT-PCR) assays were performed to detect the expression level of LINC00261 in PC cells. The location of LINC00261 in PC cells was identified by RNA fluorescence in situ hybridization (RNA-FISH). Cell Counting Kit-8 (CCK-8), cell apoptosis assay, transwell invasion and migration assays testified the critical role of LINC00261 in PC. The luciferase reporter assay was applied to confirm the binding of LINC00261 to its upstream transcription factor KLF13. The changes in LINC00261 related target protein levels were analyzed by Western blotting assay.

RESULTS

LINC00261 was significantly lower in PC tissues and was mainly concentrated in the nucleus. Overexpression of LINC00261 inhibited the invasion and migration of PC cells. Mechanistically, transcription factor KLF13 was confirmed to inhibit the epithelial-mesenchymal transition (EMT) process of PC cells by promoting the transcription of LINC00261 and suppressing the expression of metastasis-associated proteins, such as matrix metalloproteinase MMP2 and vimentin, thus inhibiting the metastasis of PC.

CONCLUSION

LINC00261 regulates PC cell metastasis through the "KLF13-LINC00261-mTOR-P70S6K1-S6" signaling pathway, which provides a significant set of potential PC therapeutic targets.

1H-NMR based metabolic study of MMTV-PyMT mice along with pathological progress to screen biomarkers for the early diagnosis of breast cancer

This study showed the common metabolic changes between BC patients and mice, which were related to pathological processes.

Polyphenols Modulating Effects of PD-L1/PD-1 Checkpoint and EMT-Mediated PD-L1 Overexpression in Breast Cancer

Investigating dietary polyphenolic compounds as antitumor agents are rising due to the growing evidence of the close association between immunity and cancer. Cancer cells elude immune surveillance for enhancing their progression and metastasis utilizing various mechanisms. These mechanisms include the upregulation of programmed death-ligand 1 (PD-L1) expression and Epithelial-to-Mesenchymal Transition (EMT) cell phenotype activation. In addition to its role in stimulating normal embryonic development, EMT has been identified as a critical driver in various aspects of cancer pathology, including carcinogenesis, metastasis, and drug resistance. Furthermore, EMT conversion to another phenotype, Mesenchymal-to-Epithelial Transition (MET), is crucial in developing cancer metastasis. A central mechanism in the upregulation of PD-L1 expression in various cancer types is EMT signaling activation. In breast cancer (BC) cells, the upregulated level of PD-L1 has become a critical target in cancer therapy. Various signal transduction pathways are involved in EMT-mediated PD-L1 checkpoint overexpression. Three main groups are considered potential targets in EMT development; the effectors (E-cadherin and Vimentin), the regulators (Zeb, Twist, and Snail), and the inducers that include members of the transforming growth factor-beta (TGF-β). Meanwhile, the correlation between consuming flavonoid-rich food and the lower risk of cancers has been demonstrated. In BC, polyphenols were found to downregulate PD-L1 expression. This review highlights the effects of polyphenols on the EMT process by inhibiting mesenchymal proteins and upregulating the epithelial phenotype. This multifunctional mechanism could hold promises in the prevention and treating breast cancer.

FENDRR: A pivotal, cancer-related, long non-coding RNA

Long non-coding RNAs (lncRNAs) have more than 200 nucleotides and do not encode proteins. Based on numerous studies, lncRNAs have emerged as new and crucial regulators of biological function and have been implicated in the pathogenesis of a variety of diseases, especially cancers. Specific lncRNAs have been identified as novel molecular biomarkers for cancer diagnosis, prognosis, and treatment efficacy. Fetal-lethal non-coding developmental regulatory RNA (FENDRR, also known as FOXF1-AS1) is a novel lncRNA that is located at chr3q13.31 and has four exons and 3099 nucleotides, and its genomic site is located at chr3q13.31. FENDRR is abnormally expressed in a variety of cancers and is significantly associated with different clinical characteristics. In addition, FENDRR has shown potential as a biomarker for cancer diagnosis, prognosis, and treatment. In this review, we summarize the current understanding of FENDRR and its mechanistic role in cancer progression. We also discuss recent insights into the clinical significance of FENDRR for cancer diagnosis, prognosis, and treatment.

MEDAG enhances breast cancer progression and reduces epirubicin sensitivity through the AKT/AMPK/mTOR pathway

Breast cancer (BC) is the most common malignancy among women. Mesenteric estrogen-dependent adipogenesis gene (MEDAG) was first reported as a novel adipogenic gene, and its involvement and mechanism in visceral adiposity were analyzed. However, the role of MEDAG in BC is unclear. The biological roles and corresponding mechanisms were investigated in vitro and in vivo. We found that MEDAG was highly expressed in BC samples and that a high MEDAG expression was correlated with clinicopathological characteristics and poor survival in BC patients. MEDAG knockdown inhibited cell proliferation, invasion, and migration; triggered epithelial-to-mesenchymal transition (EMT); and enhanced epirubicin sensitivity in vitro. The opposite results were observed in MEDAG-overexpressing cells. The inhibition of MEDAG suppressed tumor growth and metastasis in vivo. Mechanistically, MEDAG knockdown led to decreased phosphorylation levels of AKT, increased levels of p-AMPK, and reduced levels of p-mTOR, while the overexpression of MEDAG had the opposite effects. Moreover, the activation of p-AKT and inhibition of p-AMPK restored the effect of MEDAG on EMT and chemosensitivity in BC cell lines, indicating that MEDAG functions as an oncogene by regulating the AKT/AMPK/mTOR pathway. MEDAG regulates BC progression and EMT via the AKT/AMPK/mTOR pathway and reduces chemosensitivity in BC cells. Therefore, MEDAG is a promising target for BC.

Association of mTOR pathway with risk of gastric cancer in male smoker with potential prognostic significance

Aberrant expression of mTOR signaling pathway is significantly associated with gastric cancer. However, the effect of smoking on mTOR expression and its downstream signaling molecules in gastric cancer has not been explored. Our study aims to investigate the effect of smoking on p-mTOR and its correlation with various downstream targets and survival of the smoker and never-smoker in advanced gastric cancer patients. Forty-one smokers and 41 never-smokers patient sample with the advanced gastric carcinoma were chosen for this study. Immunohistochemistry and western blot analysis were performed to check the expression of p-mTOR and its downstream targets. The correlation of p-mTOR with its downstream targets was analyzed by linear regression analysis in Graph Pad Prism software. Survivability analysis was examined by Kaplan-Meier method with log rank test in SPSS. High expression of p-mTOR and its downstream targets were observed in advanced gastric cancer smoker patients as compared to never-smokers by immunohistochemistry and western blot analysis. Results revealed that over expressed p-mTOR in smoker patients were positively correlated with its downstream targets (P < 0.05) and poor survival (P = 0.034). Over expression of p-mTOR in gastric cancer male smoker patients had the worse outcome.

The Role of ALDH in the Metastatic Potential of Osteosarcoma Cells and Potential ALDH Targets

Aldehyde dehydrogenases are a family of enzymes that oxidize aldehydes to carboxylic acids. These enzymes are important in cellular homeostasis during oxidative stress by the elimination of toxic aldehyde by-products from various cellular processes. In osteosarcoma, aldehyde dehydrogenase 1A1has been described as a cancer stem cell marker. Its activity has been found to correlate with metastatic potential and the metastatic phenotype. As such, a more complete understanding of aldehyde dehydrogenase in osteosarcoma will give us a deeper knowledge of its impact on osteosarcoma metastatic potential. Our hope is that this knowledge can be translated into novel antimetastatic therapeutic strategies and thus improve osteosarcoma prognoses.

Investigation of EGFR/pi3k/Akt signaling pathway in seminomas

Activation of the receptor for epidermal growth factor (EGFR) in some testicular tumors activates several signaling pathways. Some components of these pathways are phosphorylated or mutated in testicular germ tumors (TCGT), including EGFR, Kirstein ras oncogen (KRAS) and cell surface protein of the germ cell (KIT). The latter two activate RAF ⁄MEK⁄ERK and PI3 K⁄AKT, and interconnect with the EGFR/pI3 k/Akt pathway. We investigated the expression of EGFR/pI3 k/Akt pathway proteins in seminomas and in their precursor lesion, germinal cell neoplasia in situ (GCNIS) and related genetic mutations. We used immunohistochemistry for pEGFR, pI3 k and pAkt expression with a scoring system for 46 seminoma surgical specimens: 36 classical and 10 GCNIS. In 17 samples, the mutations of EGFR (exons 19 - 21), KIT (exons 11, 17) and KRAS (exons 2, 3) were investigated using qPCR and sequencing. Of the 36 seminomas studied, 22 (61%) expressed pEGFR. Ten samples exhibited high scores for pEGFR, pI3 k and pAkt. In 5 of 17 cases (33%) some mutation was exhibited in the exons studied: 21 of EGFR (2), 17 of EGFR (1), 3 of KRAS (1) and 11 of KIT (1). Six cases exhibited nuclear translocation of EGFR; of these, four exhibited mutations of EGFR, KRAS and KIT. Eight of ten of the GCNIS expressed a high pEGFR score (80%). In 2 of 6 cases (33%), mutation was detected in exon 21 of EGFR and one smear showed EGFR translocation to the nucleus. The translocation represents a subpopulation with worse prognosis for TCGT. The EGFR/pI3 k/Akt signaling pathway is linked to TDRG1, which regulates chemosensitivity to cisplatin; this is a mechanism of resistance to treatment. TDRG1 and the EGFR/pI3 k/pAkt pathway could be therapeutic targets for seminomas resistant to cisplatin.

The Escherichia coli protein toxin cytotoxic necrotizing factor 1 induces epithelial mesenchymal transition

Some toxigenic bacteria produce protein toxins with carcinogenic signatures, which either directly damage DNA or stimulate signalling pathways related to cancer. So far, however, only a few of them have been proved to favour the induction or progression of cancer. In this work, we report that the Rho-activating Escherichia coli protein toxin, cytotoxic necrotising factor 1 (CNF1), induces epithelial to mesenchymal transition (EMT) in intestinal epithelial cells. EMT is a crucial step in malignant tumour conversion and invasiveness. In the case of CNF1, it occurs by up-regulation of the transcription factors ZEB1 and Snail1, delocalisation of E-cadherin and β-catenin, activation of the serine/threonine kinase mTOR, accelerated wound healing, and invasion. However, our results highlight that nontransformed epithelial cells entail the presence of inflammatory factors, in addition to CNF1, to acquire a mesenchymal-like behaviour. All this suggests that the surrounding microenvironment, as well as the cell type, dramatically influences the CNF1 ability to promote carcinogenic traits.

Amide-sulfamide modulators as effective anti-tumor metastatic agents targeting CXCR4/CXCL12 axis

Breast cancer is the most frequently diagnosed malignancy and the second common cause of death in women worldwide. High mortality in breast cancer is frequently associated with metastatic progression rather than the primary tumor itself. It has been recently identified that the CXCR4/CXCL12 axis plays a pivotal role in breast cancer metastasis, especially in directing metastatic cancer cells to CXCL12-riched organs and tissues. Herein, taking the amide-sulfamide as the lead structure, the second-round structural modifications to the sulfamide structure were performed to obtain more active CXCR4 modulators against tumor metastasis. Both in vivo and in vitro experiments illustrated that compound IIIe possessed potent CXCR4 binding affinity, excellent anti-metastatic and anti-angiogenetic activity against breast cancer. More importantly, in a mouse breast cancer lung metastasis model, compound IIIe exerted a significant inhibitory effect on breast cancer metastasis. Taken together, all these positive results demonstrated that developing of CXCR4 modulators is a promising strategy to mediate breast cancer metastasis.

mTOR Signaling Pathway in Cancer Targets Photodynamic Therapy In Vitro

The Mechanistic or Mammalian Target of Rapamycin (mTOR) is a major signaling pathway in eukaryotic cells belonging to the P13K-related kinase family of the serine/threonine protein kinase. It has been established that mTOR plays a central role in cellular processes and implicated in various cancers, diabetes, and in the aging process with very poor prognosis. Inhibition of the mTOR pathway in the cells may improve the therapeutic index in cancer treatment. Photodynamic therapy (PDT) has been established to selectively eradicate neoplasia at clearly delineated malignant lesions. This review highlights recent advances in understanding the role or regulation of mTOR in cancer therapy. It also discusses how mTOR currently contributes to cancer as well as future perspectives on targeting mTOR therapeutically in cancer in vitro.

Exosomes from N-Myc amplified neuroblastoma cells induce migration and confer chemoresistance to non-N-Myc amplified cells: implications of intra-tumour heterogeneity

Neuroblastoma accounts for 15% of childhood cancer mortality. Amplification of the oncogene N-Myc is a well-established poor prognostic marker for neuroblastoma. Whilst N-Myc amplification status strongly correlates with higher tumour aggression and resistance to treatment, the role of N-Myc in the aggressiveness of the disease is poorly understood. Exosomes are released by many cell types including cancer cells and are implicated as key mediators in cell-cell communication via the transfer of molecular cargo. Hence, characterising the exosomal protein components from N-Myc amplified and non-amplified neuroblastoma cells will improve our understanding on their role in the progression of neuroblastoma. In this study, a comparative proteomic analysis of exosomes isolated from cells with varying N-Myc amplification status was performed. Label-free quantitative proteomic profiling revealed 968 proteins that are differentially abundant in exosomes released by the neuroblastoma cells. Gene ontology-based analysis highlighted the enrichment of proteins involved in cell communication and signal transduction in N-Myc amplified exosomes. Treatment of SH-SY5Y cells with N-Myc amplified SK-N-BE2 cell-derived exosomes increased the migratory potential, colony forming abilities and conferred resistance to doxorubicin induced apoptosis. Incubation of exosomes from N-Myc knocked down SK-N-BE2 cells abolished the transfer of resistance to doxorubicin induced apoptosis. These findings suggest that exosomes could play a pivotal role in N-Myc-driven aggressive neuroblastoma and transfer of chemoresistance between cells.

Abbreviations: RNA = ribonucleic acid; DNA = deoxyribonucleic acid; FCS = foetal calf serum; NTA = nanoparticle tracking analysis; LC-MS = liquid chromatography–mass spectrometry; KD = knockdown; LTQ = linear trap quadropole; TEM = transmission electron microscopy

Identification of B-cell translocation gene 1-controlled gene networks in diffuse large B-cell lymphoma: A study based on bioinformatics analysis

B-cell translocation gene 1 (BTG1) is a member of the BTG/transducer of Erb family. The present study evaluated the impact of BTG1 gene expression on the clinical outcome of diffuse large B-cell lymphoma (DLBCL) and investigated potential mechanisms using the Gene Expression Omnibus (GEO) database. The gene expression profile datasets GSE31312, GSE10846, GSE65420 and GSE87371 were downloaded from the GEO database. BTG1 expression and clinicopathological data were obtained from the GSE31312 dataset. In 498 cases, the expression of BTG1 in DLBCL was associated with treatment response (χ²=19.020; P<0.001) and International Prognostic Index score (χ²=5.320; P=0.025). Using the Kaplan-Meier method, it was identified that the expression of BTG1 was associated with overall survival (OS) and progression-free survival (PFS) times. Univariate and multivariate Cox regression analysis demonstrated that BTG1 was an independent predictive factor for OS and PFS. From the overlapping analysis of 407 BTG1-associated genes and 22,187 DLBCL-associated genes, 401 genes were identified as BTG1-associated DLBCL genes. Pathway analysis revealed that BTG1-associated DLBCL genes were associated with cancer progression and DLBCL signaling pathways. Subsequently, a protein-protein interaction network was constructed of the BTG1-associated genes, which consisted of 235 genes and 601 interactions. Additionally, 24 genes with high degrees in the network were identified as hub genes, which included genes associated with ‘ribosome’ [ribosomal protein (RP) L11, RPL3, RPS29, RPL19, RPL15 and RPL12], ‘cell cycle’ (ubiquitin carboxyl extension protein 52, ATM and Ras homolog family member H), ‘mitogen-activated protein kinase pathway’ (mitogen-activated protein kinase 1), ‘histone modification’ (ASH1-like protein) and ‘transcription/translation’ (eukaryotic translation initiation factor 3 subunit E, eukaryotic translation elongation factor 1 δ, transcription termination factor 1, cAMP responsive element binding protein 1 and RNA polymerase II subunit F). In conclusion, BTG1 may serve as a predictive biomarker for DLBCL prognosis. Additionally, bioinformatics analysis indicated that BTG1 may exhibit key functions in the progression and development of DLBCL.

Long non-coding RNA in glioma: signaling pathways

Glioma is regarded as the most prevalent malignant carcinoma of the central nervous system. Thus, the development of new therapeutic strategies targeting glioma is of significant clinical importance. Long non-coding RNAs (lncRNAs) are functional RNA molecules without a protein-coding function and are reportedly involved in the initiation and progression of glioma. Dysregulation of lncRNAs in glioma is due to activation of several signaling pathways, such as the BRD4-HOTAIR-β-catenin/PDCD4, p53-Hif-H19/IGF2 and CRNDE/mTOR pathways. Furthermore, microRNAs (miRNAs) such as miR-675 also interact with lncRNAs in glioma. Thus, exploring the mechanisms by which lncRNA control processes will be instrumental for devising new effective therapies against glioma.

mTOR inhibition as an adjuvant therapy in a metastatic model of HPV+ HNSCC

Effective treatments for recurrent/metastatic human papillomavirus-positive (HPV+) head and neck squamous cell cancer (HNSCC) are limited. To aid treatment development, we characterized a novel murine model of recurrent/metastatic HPV+ HNSCC. Further analysis of the parental tumor cell line and its four recurrent/metastatic derivatives led to preclinical testing of an effective treatment option for this otherwise fatal disease. Reverse phase protein arrays identified key signaling cascades in the parental and recurrent/metastatic cell lines. While protein expression profiles differed among the recurrent/metastatic cell lines, activated proteins associated with the mTOR signaling cascade were a commonality. Based on these data, mTOR inhibition was evaluated as an adjuvant treatment for recurrent/metastatic disease. mTOR activity and treatment response were assessed in vitro by western blot, Seahorse, proliferation, clonogenic, and migration assays. Standard-of-care cisplatin/radiation therapy (CRT) versus CRT/rapamycin were compared in vivo. Low-dose rapamycin inhibited mTOR signaling, decreasing proliferation (43%) and migration (62%) while it enhanced CRT-induced cytotoxicity (3.3 fold) in clonogenic assays. Furthermore, rapamycin re-sensitized CRT-resistant, metastatic tumors to treatment in vivo, improving long-term cures (0-30% improved to 78-100%, depending on the recurrent/metastatic cell line) and limiting lymph node metastasis (32%) and lung metastatic burden (30 fold). Studies using immune compromised mice suggested rapamycin's effect on metastasis is independent of the adaptive immune response. These data suggest a role of mTOR activation in HPV+ HNSCC recurrent/metastatic disease and that adjuvant mTOR inhibition may enhance treatment of resistant, metastatic cell populations at the primary site and limit distant metastasis.

Molecular Mechanisms and Metabolomics of Natural Polyphenols Interfering with Breast Cancer Metastasis

Metastatic cancers are the main cause of cancer-related death. In breast primary cancer, the five-year survival rate is close to 100%; however, for metastatic breast cancer, that rate drops to a mere 25%, due in part to the paucity of effective therapeutic options for treating metastases. Several in vitro and in vivo studies have indicated that consumption of natural polyphenols significantly reduces the risk of cancer metastasis. Therefore, this review summarizes the research findings involving the molecular mechanisms and metabolomics of natural polyphenols and how they may be blocking breast cancer metastasis. Most natural polyphenols are thought to impair breast cancer metastasis through downregulation of MMPs expression, interference with the VEGF signaling pathway, modulation of EMT regulator, inhibition of NF-κB and mTOR expression, and other related mechanisms. Intake of natural polyphenols has been shown to impact endogenous metabolites and complex biological metabolic pathways in vivo. Breast cancer metastasis is a complicated process in which each step is modulated by a complex network of signaling pathways. We hope that by detailing the reported interactions between breast cancer metastasis and natural polyphenols, more attention will be directed to these promising candidates as effective adjunct therapies against metastatic breast cancer in the clinic.

Transcriptome Alterations In X-Irradiated Human Gingiva Fibroblasts

Ionizing radiation is known to induce genomic lesions, such as DNA double strand breaks, whose repair can lead to mutations that can modulate cellular and organismal fate. Soon after radiation exposure, cells induce transcriptional changes and alterations of cell cycle programs to respond to the received DNA damage. Radiation-induced mutations occur through misrepair in a stochastic manner and increase the risk of developing cancers years after the incident, especially after high dose radiation exposures. Here, the authors analyzed the transcriptomic response of primary human gingival fibroblasts exposed to increasing doses of acute high dose-rate x rays. In the dataset obtained after 0.5 and 5 Gy x-ray exposures and two different repair intervals (0.5 h and 16 h), the authors discovered several radiation-induced fusion transcripts in conjunction with dose-dependent gene expression changes involving a total of 3,383 genes. Principal component analysis of repeated experiments revealed that the duration of the post-exposure repair intervals had a stronger impact than irradiation dose. Subsequent overrepresentation analyses showed a number of KEGG gene sets and WikiPathways, including pathways known to relate to radioresistance in fibroblasts (Wnt, integrin signaling). Moreover, a significant radiation-induced modulation of microRNA targets was detected. The data sets on IR-induced transcriptomic alterations in primary gingival fibroblasts will facilitate genomic comparisons in various genotoxic exposure scenarios.

Anti-Breast Cancer Potential of Quercetin via the Akt/AMPK/Mammalian Target of Rapamycin (mTOR) Signaling Cascade

The Akt/adenosine monophosphate protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway has emerged as a critical signaling nexus for regulating cellular metabolism, energy homeostasis, and cell growth. Thus, dysregulation of this pathway contributes to the development of metabolic disorders such as obesity, type 2diabetes, and cancer. We previously reported that a combination of grape polyphenols (resveratrol, quercetin and catechin: RQC), at equimolar concentrations, reduces breast cancer (BC) growth and metastasis in nude mice, and inhibits Akt and mTOR activities and activates AMPK, an endogenous inhibitor of mTOR, in metastatic BC cells. The objective of the present study was to determine the contribution of individual polyphenols to the effect of combined RQC on mTOR signaling. Metastatic BC cells were treated with RQC individually or in combination, at various concentrations, and the activities (phosphorylation) of AMPK, Akt, and the mTOR downstream effectors, p70S6 kinase (p70S6K) and 4E binding protein (4EBP1), were determined by Western blot. Results show that quercetin was the most effective compound for Akt/mTOR inhibition. Treatment with quercetin at 15μM had a similar effect as the RQC combination in the inhibition of BC cell proliferation, apoptosis, and migration. However, cell cycle analysis showed that the RQC treatment arrested BC cells in the G1 phase, while quercetin arrested the cell cycle in G2/M. In vivo experiments, using SCID mice with implanted tumors from metastatic BC cells, demonstrated that administration of quercetin at 15mg/kg body weight resulted in a ~70% reduction in tumor growth. In conclusion, quercetin appears to be a viable grape polyphenol for future development as an anti BC therapeutic.

mTOR ATP-competitive inhibitor INK128 inhibits neuroblastoma growth via blocking mTORC signaling

High-risk neuroblastoma often develops resistance to high-dose chemotherapy. The mTOR signaling cascade is frequently deregulated in human cancers and targeting mTOR signaling sensitizes many cancer types to chemotherapy. Here, using a panel of neuroblastoma cell lines, we found that the mTOR inhibitor INK128 showed inhibitory effects on both anchorage-dependent and independent growth of neuroblastoma cells and significantly enhanced the cytotoxic effects of doxorubicin (Dox) on these cell lines. Treatment of neuroblastoma cells with INK128 blocked the activation of downstream mTOR signaling and enhanced Dox-induced apoptosis. Moreover, INK128 was able to overcome the established chemoresistance in the LA-N-6 cell line. Using an orthotopic neuroblastoma mouse model, we found that INK128 significantly inhibited tumor growth in vivo. In conclusion, we have shown that INK128-mediated mTOR inhibition possessed substantial antitumor activity and could significantly increase the sensitivity of neuroblastoma cells to Dox therapy. Taken together, our results indicate that using INK128 can provide additional efficacy to current chemotherapeutic regimens and represent a new paradigm in restoring drug sensitivity in neuroblastoma.

Cardamonin Inhibits Metastasis of Lewis Lung Carcinoma Cells by Decreasing mTOR Activity

The mammalian target of rapamycin (mTOR) regulates the motility and invasion of cancer cells. Cardamonin is a chalcone that exhibits anti-tumor activity. The previous study had proved that the anti-tumor effect of cardamonin was associated with mTOR inhibition. In the present study, the anti-metastatic effect of cardamonin and its underlying molecule mechanisms were investigated on the highly metastatic Lewis lung carcinoma (LLC) cells. The proliferation, invasion and migration of LLC cells were measured by MTT, transwell and wound healing assays, respectively. The expression and activation of mTOR- and adhesion-related proteins were assessed by Western blotting. The in vivo effect of cardamonin on the metastasis of the LLC cells was investigated by a mouse model. Treated with cardamonin, the proliferation, invasion and migration of LLC cells were significantly inhibited. The expression of Snail was decreased by cardamonin, while that of E-cadherin was increased. In addition, cardamonin inhibited the activation of mTOR and its downstream target ribosomal S6 kinase 1 (S6K1). Furthermore, the tumor growth and its lung metastasis were inhibited by cardamonin in C57BL/6 mice. It indicated that cardamonin inhibited the invasion and metastasis of LLC cells through inhibiting mTOR. The metastasis inhibitory effect of cardamonin was correlated with down-regulation of Snail and up-regulation of E-cadherin.

Lead toxicity induces autophagy to protect against cell death through mTORC1 pathway in cardiofibroblasts

Heavy metals, such as lead (Pb²⁺), are usually accumulated in human bodies and impair human's health. Lead is a metal with many recognized adverse health side effects and yet the molecular processes underlying lead toxicity are still poorly understood. In the present study, we proposed to investigate the effects of lead toxicity in cultured cardiofibroblasts. After lead treatment, cultured cardiofibroblasts showed severe endoplasmic reticulum (ER) stress. However, the lead-treated cardiofibroblasts were not dramatically apoptotic. Further, we found that these cells determined to undergo autophagy through inhibiting mammalian target of rapamycin complex 1 (mTORC1) pathway. Moreover, inhibition of autophagy by 3-methyladenine (3-MA) may dramatically enhance lead toxicity in cardiofibroblasts and cause cell death. Our data establish that lead toxicity induces cell stress in cardiofibroblasts and protective autophagy is activated by inhibition of mTORC1 pathway. These findings describe a mechanism by which lead toxicity may promote the autophagy of cardiofibroblasts cells, which protects cells from cell stress. Our findings provide evidence that autophagy may help cells to survive under ER stress conditions in cardiofibroblasts and may set up an effective therapeutic strategy for heavy metal toxicity.

Lead is a metal with many recognized adverse health side effects, and yet the molecular processes in cardiofibroblasts underlying lead toxicity are still poorly understood. Our current findings will help to understand the role of lead-mediated toxicity in cardiofibroblasts, indicating that autophagy serves a protective role in response to ER stress, which affords to set up an effective therapeutic strategy for the numerous diseases related to lead-toxicity.

CRNDE, a long-noncoding RNA, promotes glioma cell growth and invasion through mTOR signaling

The transcripts of the gene Colorectal Neoplasia Differentially Expressed (CRNDE) are recognized as long-noncoding RNAs (lncRNAs), which are expressed in specific regions within the human brain, and are the most upregulated lncRNA in gliomas. However, the underlying regulation and function of CRNDE in gliomas are largely unknown. In this study, the upregulation of CRNDE was confirmed in both primary specimens from glioma patients and in vitro with cell lines. Overexpression of specific CRNDE transcript promotes cell growth and migration in vitro while knockdown of CRNDE expression manifests a repressive function during these cellular processes. The growth promoting effect of CRNDE was also demonstrated in a xenograft mouse model. Mechanistic studies further revealed that histone acetylation in the promoter region might account for the upregulation of CRNDE, and the level of CRNDE expression could be modulated by mammalian Target of Rapamycin (mTOR) signaling in glioma. Thus, our results shed a light on utilizing CRNDE as a potential novel therapeutic target for the treatment of glioma.

Crosstalk between Edc4 and mammalian target of rapamycin complex 1 (mTORC1) signaling in mRNA decapping

The mammalian target of rapamycin complex 1 (mTORC1) is involved in the cellular transcription and translation processes. The undertaken study characterized the enhancer of mRNA decapping protein 4 (Edc4) as mTORC1 interacting protein. Human T lymphoblast (CCRF-CEM) cells were used for mTORC1 purification. Co-immunoprecipitation coupled with immunoblotting analysis was used to confirm the interaction of Edc4 in mTORC1 specific purifications. Further assays were incorporated to conclude the role of mTORC1 in mRNA decapping via Edc4. Edc4 was identified as a new interacting protein with mTORC1 in both the endogenous and myc-tag raptor component mTORC1 specific purifications. Quantitative co-localization using confocal microscopy demonstrated that raptor component of mTORC1 coexists with Edc4 in processing (P) bodies, a site for mRNA degradation. Incubation of cells with rapamycin, a known inhibitor of mTOR kinase activity, increased the total Edc4 protein expression but at the same time decreased the Edc4 interaction with mTORC1. Moreover, rapamycin treatment resulted in a significant decrease in total serine phosphorylated Edc4 protein signal and the total 5'-capped mRNA. These findings provide the first evidence for the pivotal role of mTORC1 in Edc4 regulation. Further in-depth studies are required to get a complete understanding of molecular crosstalk between mTORC1 signaling and mRNA decapping pathway.

mTOR Signaling in Protein Translation Regulation: Implications in Cancer Genesis and Therapeutic Interventions

mTOR is a central nutrient sensor that signals a cell to grow and proliferate. Through distinct protein complexes it regulates different levels of available cellular energy substrates required for cell growth. One of the important functions of the complex is to maintain available amino acid pool by regulating protein translation. Dysregulation of mTOR pathway leads to aberrant protein translation which manifests into various pathological states. Our review focuses on the role mTOR signaling plays in protein translation and its physiological role. It also throws some light on available data that show translation dysregulation as a cause of pathological complexities like cancer and the available drugs that target the pathway for cancer treatment.

microRNA-21-induced dissociation of PDCD4 from rictor contributes to Akt-IKKβ-mTORC1 axis to regulate renal cancer cell invasion

Renal cancer metastasis may result from oncogenic forces that contribute to the primary tumor. We have recently identified microRNA-21 as an oncogenic driver of renal cancer cells. The mechanism by which miR-21 controls renal cancer cell invasion is poorly understood. We show that miR-21 directly downregulates the proapoptotic protein PDCD4 to increase migration and invasion of ACHN and 786-O renal cancer cells as a result of phosphorylation/activation of Akt and IKKβ, which activate NFκB-dependent transcription. Constitutively active (CA) Akt or CA IKKβ blocks PDCD4-mediated inhibition and restores renal cancer cell migration and invasion. PDCD4 inhibits mTORC1 activity, which was reversed by CA IKKβ. Moreover, CA mTORC1 restores cell migration and invasion inhibited by PDCD4 and dominant negative IKKβ. Moreover, PDCD4 negatively regulates mTORC2-dependent Akt phosphorylation upstream of this cascade. We show that PDCD4 forms a complex with rictor, an exclusive component of mTORC2, and that this complex formation is reduced in renal cancer cells due to increased miR-21 expression resulting in enhanced phosphorylation of Akt. Thus our results identify a previously unrecognized signaling node where high miR-21 levels reduce rictor-PDCD4 interaction to increase phosphorylation of Akt and contribute to metastatic fitness of renal cancer cells.

Polycystin-1 and polycystin-2 are involved in the acquisition of aggressive phenotypes in colorectal cancer

The polycystins PC1 and PC2 are emerging as major players in mechanotransduction, a process that influences all steps of the invasion/metastasis cascade. We hypothesized that PC1 and PC2 facilitate cancer aggressiveness. Immunoblotting, RT-PCR, semi-quantitative and quantitative real-time PCR and FACS analyses were employed to investigate the effect of polycystin overexpression in colorectal cancer (CRC) cells. The impact of PC1 inhibition on cancer-cell proliferation was evaluated through an MTT assay. In vitro data were analyzed by Student's t-test. HT29 human xenografts were treated with anti-PC1 (extracellular domain) inhibitory antibody and analyzed via immunohistochemistry to determine the in vivo role of PC1 in CRC. Clinical significance was assessed by examining PC1 and PC2 protein expression in CRC patients (immunohistochemistry). In vivo and clinical data were analyzed by non-parametric tests, Kaplan-Meier curves, log-rank test and Cox model. All statistical tests were two-sided. PC1 overexpression promotes epithelial-to-mesenchymal transition (EMT) in HCT116 cells, while PC2 overexpression results in upregulation of the mTOR pathway in SW480 cells. PC1 inhibition causes reduced cell proliferation in CRC cells inducing tumor necrosis and suppressing EMT in HT29 tumor xenografts. In clinical study, PC1 and PC2 overexpression associates with adverse pathological parameters, including invasiveness and mucinous carcinomas. Moreover, PC1 overexpression appears as an independent prognostic factor of reduced recurrence-free survival (HR = 1.016, p = 0.03) and lowers overall survival probability, while aberrant PC2 expression predicts poor overall survival (p = 0.0468). These results support, for the first time, a direct link between mechanosensing polycystins (PC1 and PC2) and CRC progression.

The Role of PI3K/Akt/mTOR Signaling in Gastric Carcinoma

The phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway is one of the key signaling pathways induced by various receptor-tyrosine kinases. Accumulating evidence shows that this pathway is an important promoter of cell growth, metabolism, survival, metastasis, and resistance to chemotherapy. Genetic alterations in the PI3K/Akt/mTOR pathway in gastric carcinoma have often been demonstrated. Many kinds of molecular targeting therapies are currently undergoing clinical testing in patients with solid tumors. However, with the exception of the ErbB2-targeting antibody, targeting agents, including PI3K/Akt/mTOR inhibitors, have not been approved for treatment of patients with gastric carcinoma. This review summarizes the current knowledge on PI3K/Akt/mTOR signaling in the pathogenesis of gastric carcinoma and the possible therapeutic targets for gastric carcinoma. Improved knowledge of the PI3K/Akt/mTOR pathway in gastric carcinoma will be useful in understanding the mechanisms of tumor development and for identifying ideal targets of anticancer therapy for gastric carcinoma.

Heat shock protein 90 promotes epithelial to mesenchymal transition, invasion, and migration in colorectal cancer

Epithelial to mesenchymal transition (EMT), invasion, and motility are essential steps in colorectal cancer (CRC) metastasis regulated by HIF-1α and NF-κB. Since HSP90 activates HIF-1α and NF-κB, we hypothesized that inhibition of HSP90 leads to inhibition of HIF-1α and NF-κB resulting in inhibition of EMT, invasion, and motility. Treatment of colorectal cancer cell lines HT-29 and HCT-116 with ganetespib at 50 nM for 24 h inhibited EMT (downregulated vimentin and upregulated E-cadherin), matrigel invasion, and spheroid migration. Ganetespib treatment or HSP90 knockdown downregulated molecular pathways associated with EMT, invasion, and motility. The overexpression of HIF-1α or NF-κB resulted in increased EMT, invasion, and motility in both cell lines and these effects were inhibited by ganetespib. Similar effects were observed in animal xenografts treated with ganetespib. Taken together, our data demonstrate for the first time that inhibition of HSP90 downregulates both HIF-1α and NF-κB leading to inhibition of EMT, motility, and invasiveness in colorectal cancer.

Proteomics analysis of siRNA-mediated silencing of Wilms' tumor 1 in the MDA-MB-468 breast cancer cell line

The Wilms' tumor 1 (WT1) gene encodes a zinc finger which appears to be a transcriptional activator or repressor for many genes involved in cell differentiation, growth and apoptosis. In order to determine the relationship between WT1 and related proteins, WT1 was silenced with small interfering RNA (siRNA) and the protein expression pattern was analyzed by proteomics analysis including one-dimensional gel electrophoresis (1-DE) and LC-MS/MS mass spectrometry. The results revealed that 14 proteins were expressed in WT1-silenced cells (siRNA(WT1)) and 12 proteins were expressed in the WT1-expressing cells (siRNA(neg)), respectively. These proteins may be classified by their functions in apoptosis, cell signaling, protein folding, gene expression, redox-regulation, transport, structural and unknown functions. Mitogaligin, an apoptosis-related molecule, was identified when WT1 was silenced while the proteins related to the signaling pathway were detected in both siRNA(neg) and siRNA(WT1) but the type of proteins were different. For example, the IBtK protein and the SH2 domain-containing protein were present in siRNA(WT1) conditions, while the platelet-derived growth factor receptor α (PDGFRA) and Rho guanine nucleotide exchange factor 1 (Rho-GEF 1) were expressed in siRNA(neg). Of these, Rho-GEF was selected for validation by western blot analysis and demonstrated to be present only in the presence of WT1. In conclusion, WT1 is related to mitogaligin via EGFR and behaves as an anti-apoptotic molecule. Moreover, WT1 may be associated with PDGFRA and Rho-GEF 1 that activates proliferation in MDA-MB-468 cells.

Over expression of PPP2R2C inhibits human glioma cells growth through the suppression of mTOR pathway

PPP2R2C encodes a gamma isoform of the subunit B55 subfamily, which is a regulatory subunit of Protein phosphatase type 2A (PP2A). Our study shows that PPP2R2C is downregulated in glioma cells and human brain cancer patient samples. Overexpression of PPP2R2C inhibited cancer cell proliferation both in vitro and in vivo through the suppression of the activity of S6K in the mTOR pathway. Moreover, exogenous expression of PPP2R2C promoted the formation of a complex with the PP2A-C subunit to further enhance the binding of PP2A-C with S6K. Our results suggest that PPP2R2C is a potential tumor suppressor gene in human brain cancers. This study will provide novel insight into the development of therapeutic strategies in the treatment of human brain tumors.

How does cancer cell metabolism affect tumor migration and invasion?

Cancer metastasis is the major cause of cancer-associated death. Accordingly, identification of the regulatory mechanisms that control whether or not tumor cells become "directed walkers" is a crucial issue of cancer research. The deregulation of cell migration during cancer progression determines the capacity of tumor cells to escape from the primary tumors and invade adjacent tissues to finally form metastases. The ability to switch from a predominantly oxidative metabolism to glycolysis and the production of lactate even when oxygen is plentiful is a key characteristic of cancer cells. This metabolic switch, known as the Warburg effect, was first described in 1920s, and affected not only tumor cell growth but also tumor cell migration. In this review, we will focus on the recent studies on how cancer cell metabolism affects tumor cell migration and invasion. Understanding the new aspects on molecular mechanisms and signaling pathways controlling tumor cell migration is critical for development of therapeutic strategies for cancer patients.

Regulation of the mTOR-Rac1 axis in platelet function

Small GTPase proteins regulate cytoskeletal dynamics to orchestrate diverse cellular functions in organismal physiology, development and disease. The Rho GTPase family member Rac1 is central to actin-driven processes in a number of cell types, particularly platelets, where Rac1 serves as an essential mediator of lamellipodia formation and thrombus stability. Despite the importance of Rac1 to platelet function, little is known about how Rac1 activity is regulated in platelets. We recently defined the tyrosine-kinase based signaling cascade that activates mTOR to regulate Rac1 activation downstream of platelet integrin and glycoprotein receptors. We demonstrated a critical role for the mTOR-Rac1 axis in regulating platelet spreading, aggregation and aggregate stability under shear. These studies suggest that in addition to cancer and transplant medicine, intervention of the mTOR system may have implications for hemostatic and thrombotic processes as well as immunotherapies and intravascular stent design.

The HPV16 E6 oncoprotein causes prolonged receptor protein tyrosine kinase signaling and enhances internalization of phosphorylated receptor species

The high-risk human papillomavirus (HPV) E6 proteins are consistently expressed in HPV-associated lesions and cancers. HPV16 E6 sustains the activity of the mTORC1 and mTORC2 signaling cascades under conditions of growth factor deprivation. Here we report that HPV16 E6 activated mTORC1 by enhanced signaling through receptor protein tyrosine kinases, including epidermal growth factor receptor and insulin receptor and insulin-like growth factor receptors. This is evidenced by sustained signaling through these receptors for several hours after growth factor withdrawal. HPV16 E6 increased the internalization of activated receptor species, and the signaling adaptor protein GRB2 was shown to be critical for HPV16 E6 mediated enhanced EGFR internalization and mTORC1 activation. As a consequence of receptor protein kinase mediated mTORC1 activation, HPV16 E6 expression increased cellular migration of primary human epithelial cells. This study identifies a previously unappreciated mechanism by which HPV E6 proteins perturb host-signaling pathways presumably to sustain protein synthesis during the viral life cycle that may also contribute to cellular transforming activities of high-risk HPV E6 proteins.

High-risk human papillomavirus infections are associated with nearly all cases of cervical cancer. HPVs infect basal epithelial cells but virion production is restricted to the outer, terminally differentiated layers of the infected epithelia where supply of nutrients and growth factors may be limited. High-risk HPV E6 proteins have been shown to activate mTORC1 signaling and increase cap dependent translation. Here we show that HPV16 E6 activates the mTORC1 and MAP kinase signaling pathways through activating receptor protein tyrosine kinases (RPTKs) and increases EGFR internalization, even after growth factor withdrawal. The signaling adaptor protein GRB2 is a critical mediator of HPV16 E6 mediated EGFR internalization and mTORC1 activation. Lastly, we demonstrate that HPV16 E6 mediated activation of RPTK and mTORC1 signaling causes increased cellular migration even after growth factor withdrawal. These results suggest a previously unappreciated mechanism by which HPV E6 proteins may support the viral life cycle and that may contribute to the transforming activities of high-risk HPV E6 proteins. Hence, inhibition of RPTK signaling networks may be evaluated as a therapeutic strategy for HPV-associated lesions and cancers.

Rapamycin Inhibits ALDH Activity, Resistance to Oxidative Stress, and Metastatic Potential in Murine Osteosarcoma Cells

Osteosarcoma (OS) is the most common primary malignancy of bone. Mortality is determined by the presence of metastatic disease, but little is known regarding the biochemical events that drive metastases. Two murine OS cell lines, K7M2 and K12, are related but differ significantly in their metastatic potentials: K7M2 is highly metastatic whereas K12 displays much less metastatic potential. Using this experimental system, the mammalian target of rapamycin (mTOR) pathway has been implicated in OS metastasis. We also discovered that aldehyde dehydrogenase (ALDH, a stem cell marker) activity is higher in K7M2 cells than K12 cells. Rapamycin treatment reduces the expression and enzymatic activity of ALDH in K7M2 cells. ALDH inhibition renders these cells more susceptible to apoptotic death when exposed to oxidative stress. Furthermore, rapamycin treatment reduces bone morphogenetic protein-2 (BMP2) and vascular endothelial growth factor (VEGF) gene expression and inhibits K7M2 proliferation, migration, and invasion in vitro. Inhibition of ALDH with disulfiram correlated with decreased mTOR expression and activity. In conclusion, we provide evidence for interaction between mTOR activity, ALDH activity, and metastatic potential in murine OS cells. Our work suggests that mTOR and ALDH are therapeutic targets for the treatment and prevention of OS metastasis.

Skeletal metastasis: treatments, mouse models, and the Wnt signaling

Skeletal metastases result in significant morbidity and mortality. This is particularly true of cancers with a strong predilection for the bone, such as breast, prostate, and lung cancers. There is currently no reliable cure for skeletal metastasis, and palliative therapy options are limited. The Wnt signaling pathway has been found to play an integral role in the process of skeletal metastasis and may be an important clinical target. Several experimental models of skeletal metastasis have been used to find new biomarkers and test new treatments. In this review, we discuss pathologic process of bone metastasis, the roles of the Wnt signaling, and the available experimental models and treatments.

miRNA-100 inhibits human bladder urothelial carcinogenesis by directly targeting mTOR

miRNAs are involved in cancer development and progression, acting as tumor suppressors or oncogenes. In this study, miRNA profiling was conducted on 10 paired bladder cancer tissues using 20 GeneChip miRNA Array, and 10 differentially expressed miRNAs were identified in bladder cancer and adjacent noncancerous tissues of any disease stage/grade. After being validated on expanded cohort of 67 paired bladder cancer tissues and 10 human bladder cancer cell lines by quantitative real-time PCR (qRT-PCR), it was found that miR-100 was downregulated most significantly in cancer tissues. Ectopic restoration of miR-100 expression in bladder cancer cells suppressed cell proliferation and motility, induced cell-cycle arrest in vitro, and inhibited tumorigenesis in vivo both in subcutaneous and in intravesical passage. Bioinformatic analysis showed that the mTOR gene was a direct target of miR-100. siRNA-mediated mTOR knockdown phenocopied the effect of miR-100 in bladder cancer cell lines. In addition, the cancerous metastatic nude mouse model established on the basis of primary bladder cancer cell lines suggested that miR-100/mTOR regulated cell motility and was associated with tumor metastasis. Both mTOR and p70S6K (downstream messenger) presented higher expression levels in distant metastatic foci such as in liver and kidney metastases than in primary tumor. Taken together, miR-100 may act as a tumor suppressor in bladder cancer, and reintroduction of this mature miRNA into tumor tissue may prove to be a therapeutic strategy by reducing the expression of target genes.

microRNA-21 governs TORC1 activation in renal cancer cell proliferation and invasion

Metastatic renal cancer manifests multiple signatures of gene expression. Deviation in expression of mature miRNAs has been linked to human cancers. Importance of miR-21 in renal cell carcinomas is proposed from profiling studies using tumor tissue samples. However, the role of miR-21 function in causing renal cancer cell proliferation and invasion has not yet been shown. Using cultured renal carcinoma cells, we demonstrate enhanced expression of mature miR-21 along with pre-and pri-miR-21 by increased transcription compared to normal proximal tubular epithelial cells. Overexpression of miR-21 Sponge to quench endogenous miR-21 levels inhibited proliferation, migration and invasion of renal cancer cells. In the absence of mutation in the PTEN tumor suppressor gene, PTEN protein levels are frequently downregulated in renal cancer. We show that miR-21 targets PTEN mRNA 3'untranslated region to decrease PTEN protein expression and augments Akt phosphorylation in renal cancer cells. Downregulation of PTEN as well as overexpression of constitutively active Akt kinase prevented miR-21 Sponge-induced inhibition of renal cancer cell proliferation and migration. Moreover, we show that miR-21 Sponge inhibited the inactivating phosphorylation of the tumor suppressor protein tuberin and attenuated TORC1 activation. Finally, we demonstrate that expression of constitutively active TORC1 attenuated miR-21 Sponge-mediated suppression of proliferation and migration of renal cancer cells. Our results uncover a layer of post-transcriptional regulation of PTEN by transcriptional activation of miR-21 to force the canonical oncogenic Akt/TORC1 signaling conduit to drive renal cancer cell proliferation and invasion.

CMV late phase-induced mTOR activation is essential for efficient virus replication in polarized human macrophages

Human cytomegalovirus (CMV) remains one of the most important pathogens following solid-organ transplantation. Mounting evidence indicates that mammalian target of rapamycin (mTOR) inhibitors may decrease the incidence of CMV infection in solid-organ recipients. Here we aimed at elucidating the molecular mechanisms of this effect by employing a human CMV (HCMV) infection model in human macrophages, since myeloid cells are the principal in vivo targets of HCMV. We demonstrate a highly divergent host cell permissiveness for HCMV with optimal infection susceptibility in M2 but not M1 polarized macrophages. Employing an ultrahigh purified HCMV stock we observed rapamycin-independent viral entry and induction of IFN-β transcripts, but no proinflammatory cytokines or mitogen-activated protein kinases and mTOR activation early after infection. However, in the late infection phase, sustained mTOR activation was observed in HCMV-infected cells and was required for efficient viral protein synthesis including the viral late phase proteins pUL-44 and pp65. Accordingly, rapamycin strongly suppressed CMV replication 3 and 5 days postinfection in macrophages. In conclusion, these data indicate that mTOR is essential for virus replication during late phases of the viral cycle in myeloid cells and might explain the potent anti-CMV effects of mTOR inhibitors after organ transplantation.

Resveratrol enhances the antitumor effects of temozolomide in glioblastoma via ROS-dependent AMPK-TSC-mTOR signaling pathway

BACKGROUND AND PURPOSE

Resveratrol has been regarded as a promising candidate for cancer prevention and treatment. The present study was to investigate the impact of resveratrol on the antitumor effects of temozolomide (TMZ), a standard treatment regiment of glioblastoma (GBM), in vitro and in vivo.

METHODS AND RESULTS

We found that the combination of resveratrol and TMZ significantly resulted in G(2)/M cell cycle arrest by flow cytometry, triggered a robust increase in expression of astrocyte differentiation marker glial fibrillary acid protein (GFAP), downregulated the expression of matrix metalloproteinase-9 (MMP-9) by immunohistochemistry and western blot analysis as well as inhibited cell migration by scratch wound assay. Further study revealed that TMZ in combination with resveratrol remarkably increased reactive oxygen species (ROS) production, which serves as an upstream signal for AMP-activated protein kinase (AMPK) activation. Subsequently, activated AMPK inhibited mTOR signaling and downregulated antiapoptosis protein Bcl-2, which was contributed to the additive antiproliferation effects of combination treatment. In an orthotopic xenograft model of GBM, TMZ plus resveratrol treatment significantly reduced the volume of tumor, which was confirmed by decreased expression of Ki-67, a marker of proliferation index.

CONCLUSIONS

Our findings demonstrate for the first time that resveratrol can enhance TMZ-mediated antitumor effects in GBM in vitro and in vivo, via ROS-dependent AMPK-TSC-mTOR signaling pathway.

Inhibition of phosphatidylcholine-specific phospholipase C results in loss of mesenchymal traits in metastatic breast cancer cells

Introduction

Acquisition of mesenchymal characteristics confers to breast cancer (BC) cells the capability of invading tissues different from primary tumor site, allowing cell migration and metastasis. Regulators of the mesenchymal-epithelial transition (MET) may represent targets for anticancer agents. Accruing evidence supports functional implications of choline phospholipid metabolism in oncogene-activated cell signaling and differentiation. We investigated the effects of D609, a xanthate inhibiting phosphatidylcholine-specific phospholipase C (PC-PLC) and sphingomyelin synthase (SMS), as a candidate regulator of cell differentiation and MET in the highly metastatic BC cell line MDA-MB-231.

Methods

PC-PLC expression and activity were investigated using confocal laser scanning microscopy (CLSM), immunoblotting and enzymatic assay on human MDA-MB-231 compared with MCF-7 and SKBr3 BC cells and a nontumoral immortalized counterpart (MCF-10A). The effects of D609 on PC-PLC and SMS activity, loss of mesenchymal markers and changes in migration and invasion potential were monitored in MDA-MB-231 cells by enzymatic assays, CLSM, immunoblotting and transwell chamber invasion combined with scanning electron microscopy examinations. Cell proliferation, formation and composition of lipid bodies and cell morphology were investigated in D609-treated BC cells by cell count, CLSM, flow-cytometry of BODIPY-stained cells, nuclear magnetic resonance and thin-layer chromatography.

Results

PC-PLC (but not phospholipase D) showed 2- to 6-fold activation in BC compared with nontumoral cells, the highest activity (up to 0.4 pmol/μg protein/min) being detected in the poorly-differentiated MDA-MB-231 cells. Exposure of the latter cells to D609 (50 μg/mL, 24-72 h) resulted into 60-80% PC-PLC inhibition, while SMS was transiently inhibited by a maximum of 21%. These features were associated with progressive decreases of mesenchymal traits such as vimentin and N-cadherin expression, reduced galectin-3 and milk fat globule EGF-factor 8 levels, β-casein formation and decreased in vitro cell migration and invasion. Moreover, proliferation arrest, changes in cell morphology and formation of cytosolic lipid bodies typical of cell differentiation were induced by D609 in all investigated BC cells.

Conclusions

These results support a critical involvement of PC-PLC in controlling molecular pathways responsible for maintaining a mesenchymal-like phenotype in metastatic BC cells and suggests PC-PLC deactivation as a means to promote BC cell differentiation and possibly enhance the effectiveness of antitumor treatments.

Inhibition of chemokine (CXC motif) ligand 12/chemokine (CXC motif) receptor 4 axis (CXCL12/CXCR4)-mediated cell migration by targeting mammalian target of rapamycin (mTOR) pathway in human gastric carcinoma cells

CXCL12/CXCR4 plays an important role in metastasis of gastric carcinoma. Rapamycin has been reported to inhibit migration of gastric cancer cells. However, the role of mTOR pathway in CXCL12/CXCR4-mediated cell migration and the potential of drugs targeting PI3K/mTOR pathway remains unelucidated. We found that CXCL12 activated PI3K/Akt/mTOR pathway in MKN-45 cells. Stimulating CHO-K1 cells expressing pEGFP-C1-Grp1-PH fusion protein with CXCL12 resulted in generation of phosphatidylinositol (3,4,5)-triphosphate, which provided direct evidence of activating PI3K by CXCL12. Down-regulation of p110β by siRNA but not p110α blocked phosphorylation of Akt and S6K1 induced by CXCL12. Consistently, p110β-specific inhibitor blocked the CXCL12-activated PI3K/Akt/mTOR pathway. Moreover, CXCR4 immunoprecipitated by anti-p110β antibody increased after CXCL12 stimulation and G(i) protein inhibitor pertussis toxin abrogated CXCL12-induced activation of PI3K. Further studies demonstrated that inhibitors targeting the PI3K/mTOR pathway significantly blocked the chemotactic responses of MKN-45 cells triggered by CXCL12, which might be attributed primarily to inhibition of mTORC1 and related to prevention of F-actin reorganization as well as down-regulation of active RhoA, Rac1, and Cdc42. Furthermore, rapamycin inhibited the secretion of CXCL12 and the expression of CXCR4, which might form a positive feedback loop to further abolish upstream signaling leading to cell migration. Finally, we found cells expressing high levels of cxcl12 were sensitive to rapamycin in its activity inhibiting migration as well as proliferation. In summary, we found that the mTOR pathway played an important role in CXCL12/CXCR4-mediated cell migration and proposed that drugs targeting the mTOR pathway may be used for the therapy of metastatic gastric cancer expressing high levels of cxcl12.